Selective Leaching of Phosphorus from Phosphate Tailings and Extraction of Calcium Phosphates : Toward Comprehensive Utilization of Tailing Resources

To extract phosphorus (P) and realize large-scale resource utilization of phosphate tailings, the hydrochloric acid leaching-precipitation method was employed. Namely, the P-rich fluorapatite in phosphate tailings was dissolved selectively, and then the calcium phosphates were precipitated from the leaching liquor by adjusting pH value. The results showed that P was predominantly concentrated in fluorapatite, and its dissolution ratio increased with the decrease in pH during selective leaching. At pH 1.0, the dissolution efficiency of P from phosphate tailings reached 96.3%, along with the majority of Mg and Ca. However, Si was hardly dissolved. It demonstrated that almost all the fluorapatite and dolomite were dissolved while the quartz was difficult to dissolve. Dolomite was more preferentially dissolved than fluorapatite. Increasing temperature contributed to the dissolution of dolomite while suppressing fluorapatite dissolution. The residue obtained after leaching was found to contain 87.9% SiO2 (quartz) and only 0.25% P2O5, which can be used as a construction material. As the pH increased to 7.0, the P concentration in leaching liquor was extremely low because of the precipitation of calcium phosphates. The precipitate, which contains 34.18% P2O5 and 56.10% CaO, can serve as a source of a slow-released phosphate fertilizer. The high-efficient utilization of phosphate tailings was achieved via this process